Halogenated polyethylene coated crystalline explosive mixed with second explosive

ABSTRACT

SHAPED HIGH EXPLOSIVES PREPARED BY COATING A PARTICULATE CRYSTALLINE EXPLOSIVE HAVING A MELTING POINT OF AT LEAST 203*C. WITH A HALOGENATED POLYETHYLENE BY MIXING THE CRYSTALLINE EXPLOSIVE PARTICLES WITH AN AQUEOUS DISPRESION OF ISCRETE HALOGENATED POLYETHYLENE PARTICLES HAVING AN AVERAGE SIZE OF 0.1 TO 5 MICRONS TO DISTRIBUTE OVER THE CRYSTALLINE EXPLOSIVE PARTICLES ABOUT 2 TO 8 PERCENT BY WEIGHT OF HALOGENATED POLYETHYLENE PARTICLES, MIXING THE HALOGENATED POLYETHYLENE COATED CRYSTALLINE EXPLOSIVE PARTICLES WITH ABOUT 2 TO 8 PERCENT BY WEIGHT OF A SECOND EXPLOSIVE HAVING A MELTING POINT UP TO 105*C. AND HAVING A TRAUZL LEAD-BLOCK EXPRESION HIGHER THAN THAT OF TRINITROTOLUENE AND COMPRESSING THE MIXTURE AT A COMPRESSIVE LOAD OF AT LEAST 700 KP./CM.2 AND A TEMPERATURE ABOVE THE MELTING POINT OF THE SECOND EXPLOSIVE.

United States Patent HALOGENATED POLYETHYLENE COATED CRYS- TALLINEEXPLOSIVE MIXED WITH SECOND EXPLOSIVE Robert Sakreis, Jettenbach, andHelmuth Nolte, Waldkraiburg, Germany, assignors to Wasagchemie G.m.b.H.,Munich, Germany No Drawing. Filed Apr. 11, 1972, Ser. No. 243,080

Claims priority, application Germany, May 6, 1971, P 21 22 441.9 Int.Cl. C06b 19/02 US. Cl. 149-11 8 Claims ABSTRACT OF THE DISCLOSURE Shapedhigh explosives prepared by coating a particulate crystalline explosivehaving a melting point of at least 203 C. with a halogenatedpolyethylene by mixing the crystalline explosive particles with anaqueous dispersion of discrete halogenated polyethylene particles havingan average size of 0.1 to microns to distribute over the crystallineexplosive particles about 2 to 8 percent by weight of halogenatedpolyethylene particles, mixing the halogenated polyethylene coatedcrystalline explosive particles with about 2 to 8 percent by weight of asecond explosive having a melting point up to 105 C. and having a Trauzllead-block expansion higher than that of trinitrotoluene and compressingthe mixture at a compressive load of at least 700 kp./cm. and atemperature above the melting point of the second explosive.

BACKGROUND OF THE INVENTION The field of the invention is explosivearticle shaping or treating by coating the base explosive with anorganic compound.

The state of the art of explosives useful in the present invention andthe testing and physical properties thereof may be ascertained byreference to the Kirk-Othmer Encyclopedia of Chemical Technology, 2nded., vol. 8 (1965), pages 581 to 658, particularly pages 622-624 whichdisclose cyclotrimethylenetrinitramine andcyclotetramethylenetetranitramine, pages 632-633 which disclose thesensitivity and explosive characteristics of high explosives, and pages654-658 which disclose testing methods for explosives.

The disclosures of the following U.S. patents which show the state ofthe art of desensitizing high explosives by coating the crystallineparticulate explosives with various materials are incorporated herein:

3,466,204, Gow, which issued Sept. 9, 1969; 3,544,360, Gardner, whichissued Dec. 1, 1970; 3,000,720, Baer, which issued Sept. 19, 1961;3,348,986, Sauer, which issued Oct. 24, 1967; 3,291,666, Thatcher, whichissued Dec. 13, 1966; and 3,496,041, Riedl, which issued Feb. 17, 1970.

Gow discloses a method of desensitizing explosives wherein discreteparticles of an explosive composition are coated withpolytetrafluoroethylene by mixing the explosive composition particleswith an aqueous dispersion of discrete polytetrafluoroethylene particleshaving an average size of 0.1 to 5 microns to distribute over thesurfaces of the explosive composition particles 1-5 percent by weight ofpolytetrafluoroethylene particles and in which the coated particles arecompressed to convert them to a coherent mass. Gow also discloses that asuitable 60 percent aqueous dispersion of polytetrafiuoroethylene iscommercially available as Fluon, Grade GPI.

Cyclonite particles coated with latex to be pressed or shaped aredisclosed in the patent to Sauer. Baer discloses the coating ofCyclonite with dinitroethylbenzene to desensitize the explosive. Gardnerdiscloses the coating of Cyclonite and Octogen with wax.

According to the patent of Thatcher, readily pressed explosivecompositions of high thermal stability consisting essentially ofcrystalline organic compounds having a melting point of at least 325 F.selected from the group consisting of picryl sulfone, Cyclonite andOctogen are prepared by admixing with vinylidene fluoride orhexafluoropropylene in a concentration of 1-5 percent by weight.

The present invention is related particularly to a shaped high explosiveof a high density, high strength, and high detonating velocity basedupon high melting and high efiiciency components, such ascyclotetramethylenetetranitramine and cyclotrimethylenetrinitramine.

The chemistry of explosives encompasses, especially in the series of thealiphatic nitramines, substances having very high efiiciencies, whichare relatively safe in handling and simultaneously exhibit asatisfactory chemical stability. It seems to be irrefutable that theoptimum compound in this connection is cyclotetramethylenetetranitramine(Octogen, HMX), the fi-isomer of which has a maximum density of 1.92 ascompared to 1.64 for trinitrotoluene (TNT). HMX detonates at adetonating velocity which is above 9,000 m./sec. for a density of 1.90.Similarly favorable efficiency values are demonstrated by the relatedcompound cyclotrimethylenetrinitramine (Hexogen, Cyclonite, RDX), with adetonating velocity of 8,400 m./ sec. (at a density of 1.70) and amaximum density of 1.82. In contrast to the standard explosive formilitary purposes, namely trinitrotoluene, the above-mentionedsubstances cannot be directly cast into shape. The melting points are ashigh (Octogen 282 C., Cyclonite 203 C.) that the substances aredecomposed during the melting step. The aforementioned compounds cannotbe shaped, even by means of presses, without providing additives, sincethere is no binding power from crystal to crystal, and when very highcompressive pressures are used, there is the danger of an explosion. Incontrast thereto, TNT can be cast (M.P. C.) or pressed withoutadditives.

The problem of shape-casting these high melting, high explosives hasbeen solved for a long time in various ways. The substances werestabilized, i.e. provided with an addition of wax and shaped andcompressed by means of presses in this form, as disclosed in US. Pat.3,544,- 360. In this connection, the Wax serves to markedly re duce theimpact sensitivity, as well as serving as a binder between the explosivecrystals in the structure produced by the pressing step. In accordancewith another method, the high melting explosive components areintroduced into the melt of a lower melting explosive, preferablytrinitrotoluene, and shaped by casting in this pasty form. Finally,shape casts have been successfully performed by introducing the highmelting explosive into a liquid synthetic resin which has not as yetbeen cross-linked, and by-curing the synthetic resin binder with the useof curing agents and catalysts. According to German Pat. 1,172,590natural rubber was used as the binder and the rubber was 'vulcanizedafter the explosive had been incorporated with TNT amenable to casting,much effort has been expended to raise the content of the high meltingmaterial to as high a level as possible by means of special castingmethods (e.g. by the use of prolonged sedimentation, by pretreating themelt under vacuum and casting under pressure, by the use of positiveforces, such as centrifugal action or pressing by means of screensurfaces), and thus to attain high densities and high detonationvelocities.

The use of non-brisant binders does not always have a stabilizingeffect. In certain Cyclonite and Octogen shape-castings bound with aplastic, a rather high impact sensitivity and firing sensitivity wassurprisingly observed.

SUMMARY OF THE INVENTION Therefore, it is an object of the presentinvention to propose a shaped high explosive and a process for thepreparation thereof, wherein the aforementioned disadvantages areavoided. According to the present invention, the data relating to theexplosive technology, particularly the density and the detonatingvelocity of the high efiiciency basic explosives, are retained in theirfull values or remain at almost the same level, but wherein, on theother hand, the sensitivity characteristics are markedly reduced and ashaped explosive is produced having a surprisingly high mechanicalstrength.

According to the present invention, the shaped high explosive ischaracterized in that the basic explosive, present in crystalline form,is coated with 2-8 percent by weight of a plastic selected from thegroup consisting of the halogenated polyethylenes, by treatment in anaqueous dispersion of the plastic; dried; mixed with another 8-2 percentof an explosive having a melting point up to 105 C. and having a Trauzllead-block expansion higher than that of trinitrotoluene; and exposingthe composition, at temperatures above the melting point of the addedexplosive, to a compressive load of at least 700 kp./cm.

TNT is used as the basis for the Trauzl lead-block test wherein TNT israted as 100 percent and Cyclonite and HMX are rated as 170 percent and153 percent respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Advantageously, the plasticfrom the group of halogenated polyethylene consists ofpolytetrafluoroethylene and polychlorotrifluoroethylene.

Specific examples of the commercially available halogenatedpolyethylenes include: Fluon, Grade GPI (60 percent aqueous dispersionof polytetrafluoroethylene having a particle size of 0.1 to microns):Hostaflon (polytrifiuoromonochloroethylene); Trithene (polytrifluoromonochloroethylene); Voltalef (polytrifiuoromonochloroethylene);Teflon (polytetrafluoroethylene); Hostaflon TF(polytetrafluoroethylene).

In a preferred embodiment of the invention, the brisant component whichdoes not melt above 105 C. and has a Trazul lead-block test over 100consists of aromatic nitramines or mixtures thereof, or nitrates high innitrogen, such as hydrazine nitrate, trinitrophenylethylnitramine,trinitrophenylmethylnitramine, trinitrochlorobenzene and mixturesthereof.

The brisant component, in this connection, exhibits the property of anactive binder.

The particulate crystalline high explosives of the present inventionhave a grain size of about 40 to 800 mi crons and include:cyclotetramethylenetetranitramine having a melting point of 282 C.; andcyclotrimethylenetrinitramine having a melting point of 203 C.

The process for the production of the high efficiency explosive consistsof exposing the mixture of the basic explosive coated by treatment withan aqueous dispersion of a halogenated polyethylene and then dried, andof an explosive which does not melt above 105 C. and has a higher Trazullead-block expansion than trinitrotoluene at temperatures above themelting point of the added explosive, to a shaping pressure of at least700 kp./cm. The pressure is maintained during the subsequent coolingperiod until the added, lower melting explosive has passed over from theliquid phase into the solid phase. Thereby, a space filling of more than99.5 percent is achieved and thus the highest possible density isattained which, in turn, is the prerequisite for a high detonatingvelocity. Furthermore, an advantage in this connection is to select, forthis purpose, as the active binder a substance having a satisfactoryinherent explosive capacity and, as the plastic binder, a substancehaving a high density, such as polytetrafluoroethylene orpolychlorotrifluoroethylene. The pressure range is preferably 700kp./cm. to 2000 kp./cm.

The firing sensitivity of the shaped explosive of this invention issurprisingly low (the explosive was subjected to a rifle bullet impacttest with 6.2 x 54 mm. ammunition having a V (muzzle velocity of 1000m./sec.). Smooth penetrations by the projectiles could be obtainedwithout any noticeable reaction, although in accordance with experiencegained otherwise with plastic-bound explosive compositions, positivefiring sensitivities were to be expected. In the case of pure plasticbinding procedures in the casting and cross-linking process, thepercussion-sensitive grain of the high explosive Octogen is embedded inan unmeltable bond. However, according to the present invention, thegrain is first encased with the plastic and then shaped in a pressingstep together with a meltable active binder. Thus, the impact energy ofthe projectile is at least partially converted into heat for melting theactive binder and, by the incipient melting of the active binder.Thereby a sliding yieldability of the impact-sensitive high explosiveparticles is attained.

The invention will be explained by the following examples.

EXAMPLE 1 900 g. of cyclotetramethylenetetranitramine (Octogen) having agrain size of 40-800 microns is introduced into 3 liters of a 1.5percent strength aqueous dispersion of polychlorotrifluoroethylene andthoroughly agitated until the water of dispersion has become clear andthe plastic material has been precipitated on the crystalline surfacesof the Octogen. The Octogen thus impregnated with 5 percent of syntheticresin is sucked-off, dried, and mixed with 45 g. of finely crystallinetrinitrophenylethylnitramine (corresponding to 5 percent), and pressedat C. (somewhat above the melting point of trinitrophenylethylnitramine)with a pressure of 1,600 kp./cm. The pressure is maintained (by means ofa press or of a die which is locked and provided with compressionsprings) until the trinitrophenylethylnitramine, which has entered intoa state of melt flux, is again solidified. The densities attained inthis connection exceed achieved with 99.5 percent possible spacefilling. After ejection, a shaped article is obtained, the density ofwhich is 1.88 g./cm. having a detonating velocity of 8,850 m./sec., aBrinell hardness of 32-34, and a compressive strength of 46 kg./cm. Inthe determination of the firing sensitivity, no explosion is producedwith several shots using 6.5 x 57 mm. ammunition, partial shell-S(pointed) without a blasting charge and with a V of 1,000 m./ sec.

EXAMPLE 2 900 g. of cyclotrimethylenetrinitramine (Cyclonite) having thesame grain size as set forth in Example 1 is treated in the same mannerwith 3 liters of a 1.8 percent strength aqueous dispersion ofpolytetrafluoroethylene. The Cyclonite thus impregnated with 6 percentof plastic is sucked-off, dried, and mixed with 36 g. (corresponding to4 percent), of a fine crystalline mixture of 30 percenttrinitrophenylmethylnitramine (tetryl) and 70 percent oftrinitrophenylethylnitramine (ethyl tetryl) and pressed at 103 C.(somewhat above the melting point of the mixture) at a pressure of 1,200kp./cm. and the pressure is again maintained until the mixture hassolidified. The pressed article obtained exhibits a density of 1.81, adetonating velocity of 8,600 m./sec. (literature value for pureCyclonite=8,400 m./sec.), a Brinell hardness of 32-34, and a compressivestrength of 45 kg./cm. In the determination of the firing sensitivity,no explosion occurs when several shots are fired into it with 6.5 x 57mm. ammunition without explosive charge and at a V of 1,000 m./sec.

EXAMPLE 3 900 g. of Octogen of the same grain size as set forth inExample 1 is impregnated with a 4 percent polychlorotrifiuoroethylene,mixed with 56 g. (corresponding to 6 percent) of hydrazine nitrate andpressed at 73 C. (somewhat above the melting point of hydrazine nitrate)at a pressure of 900 kp./cm. until the mixture has cooled. The followingdata are determined: density 1.79; detonating velocity 8,900 m./sec.;Brinell hardness 26-28; compressive strength 38 kg./cm. In a firing testconducted in the same manner as described above, no explosion isobtained with 6.5 x 57 mm. ammunition in several shots.

EXAMPLE 4 900 g. of Cyclonite of the same grain size as described inExample 1 is prepared with 7 percent of polytetrafluoroethylene in themanner described in Example 1 and mixed with 27 g. (corresponding to 3percent) of trinitrochlorobenzene (M.P. 82 C.) and then pressed at 84 C.at a pressure of 1,500 kp./cm. until the mixture has cooled. The datadetermined in this procedure are as follows: density 1.82; detonatingvelocity 8,600 m./sec.; Brinell hardness 28-30; compressive strength 48kg./cm. When the firing sensitivity is determined in the aforementionedmanner, there is no explosion or defiagration.

We claim:

1. A readily pressed explosive composition of high thermal stabilitycomprising a particulate crystalline explosive having a melting point ofat least 203 C. coated with about 2 to 8 percent by weight ofhalogenated polyethylene and admixed with a binder of about 2 to 8percent by weight of a second explosive having a melting point up to 105C., said particulate crystalline explosive selected from the groupconsisting of cyclotetramethylenetetranitramine,cyclotrimethylenetrinitramine, and triaminoguanidine nitrate and saidsecond explosive selected from the group consisting of hydrazinenitrate, trinitrophenylmethylnitramine, trinitrophenylethylnitramine,trinitrochlorobenzene and mixtures thereof.

2. The composition of claim 1, wherein said halogenated polyethylene isselected from the group consisting of polytetrafluoroethylene andpolychlorotrifluoroethylene.

3. The composition of claim 2, wherein said halogenated polyethyleneparticles have an average size of about 0.1 to 5 microns.

4. The composition of claim 1, wherein said particulate crystallineexplosive has an average size of about 40 to 800 microns.

5. A readily pressed explosive composition of high thermal stabilitycomprising a particulate crystalline explosive having a melting point ofat least 203 C. coated with about 2 to 8 percent by weight ofhalogenated polyethylene and admixed with a binder of about 2 to 8percent by weight of a second explosive having a melting point up to C.,said particulate crystalline explosive comprising an aliphatic nitramineand said second explosive comprising an aromatic nitramine.

6. A shaped high efliciency explosive of high density, high strength andhigh detonating velocity comprising a particulate crystalline explosivehaving a melting point of at least 203 C. coated with about 2 to 8percent by weight of halogenated polyethylene and bonded with a secondexplosive having a melting point up to 105 C., said particulatecrystalline explosive selected from the group consisting of aliphaticnitramines and triaminoguanidine nitrate.

7. The shaped high efiiciency explosive of claim 6, wherein saidparticulate crystalline explosive is cyclotetramethylenetetranitramineand said second explosive is selected from the group consisting ofhydrazine nitrate, trinitrophenylmethylnitramine,trinitrophenylethylnitramine, trinitrochlorobenzene and mixturesthereof.

8. The shaped high efficiency explosive of claim 6, wherein saidparticulate crystalline explosive is cyclotrimethylenetrinitramine andsaid second explosive is selected from the group consisting of hydrazinenitrate, trinitrophenylmethylnitramine, trinitrophenylethylnitramine,trinitrochlorobenzene and mixtures thereof.

References Cited UNITED STATES PATENTS 6/ 1967 Noddin 149--92 X 7/1969Gow 149-11 X LELAND A. SEBASTIAN, Primary Examiner

